SiC single crystals are thermally and chemically very stable, superior in mechanical strength, and resistant to radiation, and also have superior physical properties, such as high breakdown voltage and high thermal conductivity, compared to Si single crystals. They are therefore able to exhibit high output, high frequency, voltage resistance and environmental resistance that cannot be realized with existing semiconductor materials, such as Si single crystals and GaAs single crystals, and are being considered ever more promising as next-generation semiconductor materials for a wide range of applications including power device materials that allow high power control and energy saving, device materials for high-speed large volume information communication, high-temperature device materials for vehicles, radiation-resistant device materials and the like.
Typical growth processes for growing SiC single crystals that are known in the prior art include gas phase processes, the Acheson process, and solution processes. Among gas phase processes, for examples, sublimation processes have drawback in that grown single crystals have been prone to hollow penetrating defects known as “micropipe defects”, lattice defects, such as stacking faults, and generation of polymorphic crystals. However, most SiC bulk single crystals are conventionally produced by sublimation processes because of the high crystal growth rate, with attempts being made to reduce defects in the grown crystals. In the Acheson process, heating is carried out in an electric furnace using silica stone and coke as starting materials, and therefore it has not been possible to obtain single crystals with high crystallinity due to impurities in the starting materials.
Solution processes are processes in which molten Si or an alloy melted in molten Si is formed in a graphite crucible and C is dissolved from the graphite crucible into the molten liquid, and a SiC crystal layer is deposited and grown on a seed crystal substrate set in the low temperature section. Solution processes are most promising for reducing defects because crystal growth is carried out in a state of near thermal equilibrium, compared to gas phase processes. Recently, therefore, methods for producing SiC single crystals by solution processes have been proposed.
However, numerous technical problems still remain for obtaining large-area SiC crystals by solution processes, at high quality and with a high growth rate. A particular technical problem in regard to achieving high quality of SiC that has been noted is generation of inclusions in the SiC crystal during growth of the SiC single crystal.
Inclusions are generated by involving the Si—C solution used for SiC single crystal growth in the grown crystal. Generation of inclusions constitutes macrodefects for a single crystal, and these are unacceptable for device materials.
For the purpose of providing a method for producing a SiC single crystal capable of producing a high-quality SiC single crystal at high speed that has no inclusions in the crystal, there has been disclosed a method for producing a SiC single crystal by a solution process, wherein a molten liquid is stirred in a crucible by periodically changing the rotational speed or the rotational speed and rotational direction of the crucible (PTL 1).